Microwave circuits and more particularly distributed microwave circuits are disclosed. Such circuits and associated methods are applicable to telecommunications and other industries in which signals are processed.
Conventional circuits use lumped elements cascaded with isolated separate signal paths. Distributed integrated systems and circuits may rely on shared signal paths that may result in strong electromagnetic couplings between circuit components. A distributed amplifier includes a shared input transmission line and a shared output transmission line. A plurality of transistors, such as field-effect transistors (FETs), connect the input and output transmission lines at spaced locations and provide gain through multiple signal paths. A signal on the input transmission line, also referred to as a gate transmission line, is amplified by each transistor. An incident wave on the output transmission line, also referred to as a drain transmission line, travels toward the output in synchronization with the traveling wave on the input line. Each transistor adds power in-phase to the signal at each tap point on the output line. A forward-traveling wave on the gate line and any backward-traveling wave on the drain line are absorbed by terminations matched to the loaded characteristic impedance of the input line and output line, respectively, to avoid reflections.
Since FETs have intrinsic input capacitance and output capacitance, in general, the presence of these capacitances limits the bandwidth of operation of the FET when used in a conventional amplifier. However, with the distributed approach, the input and output capacitances of the FET become part of the propagation networks forming artificial transmission lines. In this manner, major band-limiting effects of the input and output capacitances of the transistors in reducing frequency bands of operation of the amplifier may be avoided.